Author Topic: Exoplanets And Stars Thread  (Read 23833 times)

Offline CuddlyRocket

Re: Exoplanets And Stars Thread
« Reply #200 on: 09/08/2017 11:00 PM »
A System of Three Super Earths Transiting the Late K-Dwarf GJ 9827 at Thirty Parsecs (arXiv)

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We report the discovery of three small transiting planets orbiting GJ 9827, a bright (K = 7.2) nearby late K-type dwarf star. GJ 9827 hosts a 1.64+0.22−0.20 R⊕ super Earth on a 1.2 day period, a 1.29+0.17−0.16 R⊕ super Earth on a 3.6 day period, and a 2.08+0.28−0.26 R⊕ super Earth on a 6.2 day period. The radii of the planets transiting GJ 9827 span the transition between predominantly rocky and gaseous planets, and GJ 9827 b and c fall in or close to the known gap in the radius distribution of small planets between these populations. At a distance of ∼30 parsecs, GJ 9827 is the closest exoplanet host discovered by K2 to date, making these planets well-suited for atmospheric studies with the upcoming James Webb Space Telescope. The GJ 9827 system provides a valuable opportunity to characterize interior structure and atmospheric properties of coeval planets spanning the rocky to gaseous transition.

The 'known gap' is the so-called Fulton Gap. I guess the name hasn't stuck with the wider astronomical community (yet?). :)

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #201 on: 09/11/2017 07:15 PM »
Gravitational Waves will let us see Inside Stars as Supernovae Happen

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However, according to a team of astronomers from Glasgow and Arizona, astronomers need not limit themselves to detecting waves caused by massive gravitational mergers. According to a study they recently produced, the Advanced LIGO, GEO 600, and Virgo gravitational-wave detector network could also detect the gravitational waves created by supernova. In so doing, astronomers will able to see inside the hearts of collapsing stars for the first time.

The study, titled “Inferring the Core-Collapse Supernova Explosion Mechanism with Three-Dimensional Gravitational-Wave Simulations“, recently appeared online. Led by Jade Powell, who recently finished her PhD at the Institute for Gravitational Research at the University of Glasgow, the team argue that current gravitational wave experiments should be able to detect the waves created by Core Collapse Supernovae (CSNe).

https://www.universetoday.com/137068/gravitational-waves-will-let-us-see-inside-stars-supernovae-happen/amp/

Online redliox

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Re: Exoplanets And Stars Thread
« Reply #202 on: 09/12/2017 12:06 AM »
How large does a scope need to be to directly image one of the nearer exoplanets?

Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in.  Anyone able to crunch the numbers?
"Let the trails lead where they may, I will follow."
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Offline jebbo

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Re: Exoplanets And Stars Thread
« Reply #203 on: 09/12/2017 11:07 AM »
How large does a scope need to be to directly image one of the nearer exoplanets?

Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in.  Anyone able to crunch the numbers?

You really don't need that large a telescope (assuming space based).  The key things are the Inner Working Angle and contrast ratio between the star and planet.

For example, MAPLE-150 (1.5m) would be able to resolve epsilon Eridani b:
http://www.nuvucameras.com/wp-content/uploads/2014/09/91432R.pdf

--- Tony

Online redliox

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Re: Exoplanets And Stars Thread
« Reply #204 on: 09/12/2017 06:11 PM »
How large does a scope need to be to directly image one of the nearer exoplanets?

Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in.  Anyone able to crunch the numbers?

You really don't need that large a telescope (assuming space based).  The key things are the Inner Working Angle and contrast ratio between the star and planet.

For example, MAPLE-150 (1.5m) would be able to resolve epsilon Eridani b:
http://www.nuvucameras.com/wp-content/uploads/2014/09/91432R.pdf

--- Tony

That's hopeful.  I believe I can understand what you mean by ratio (such as how a bright distant Jupiter might be easier to detect that a dark SuperEarth), but elaborate on IWA.  What else would allow an exoplanet to be more than a pixel in an image as well?
"Let the trails lead where they may, I will follow."
-Tigatron

Offline as58

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Re: Exoplanets And Stars Thread
« Reply #205 on: 09/12/2017 07:40 PM »
How large does a scope need to be to directly image one of the nearer exoplanets?

Let's assume we're targeting Epsilon Eridani's planet and the 'scope has a coronograph built in.  Anyone able to crunch the numbers?

You really don't need that large a telescope (assuming space based).  The key things are the Inner Working Angle and contrast ratio between the star and planet.

For example, MAPLE-150 (1.5m) would be able to resolve epsilon Eridani b:
http://www.nuvucameras.com/wp-content/uploads/2014/09/91432R.pdf

--- Tony

That's hopeful.  I believe I can understand what you mean by ratio (such as how a bright distant Jupiter might be easier to detect that a dark SuperEarth), but elaborate on IWA.  What else would allow an exoplanet to be more than a pixel in an image as well?

IWA is the smallest angle where at least 50% percent of the light is transmitted by the coronagraph; at smaller angles most of the light from the planet is blocked along with stellar light. Best coronagraph designs achieve IWA of about 2*lambda/D. But if you mean by "resolving" seeing the planet as something other than just a single pixel, much bigger telescopes are needed.

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #206 on: 09/13/2017 08:48 PM »
Boiling exoplanet has titanium atmosphere

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The exoplanet WASP-19b has huge amounts of titanium oxide in its atmosphere, causing the atmosphere to 'reverse' so some of the upper layers are warmer than those lower down.

http://m.skyatnightmagazine.com/news/boiling-exoplanet-has-titanium-atmosphere

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #207 on: 09/15/2017 07:18 PM »
NASA's Hubble Captures Blistering Pitch-Black Planet
NASA's Hubble Space Telescope has observed a planet outside our solar system that looks as black as fresh asphalt because it eats light rather than reflecting it back into space. This light-eating prowess is due to the planet's unique capability to trap at least 94 percent of the visible starlight falling into its atmosphere.

The oddball exoplanet, called WASP-12b, is one of a class of so-called "hot Jupiters," gigantic, gaseous planets that orbit very close to their host star and are heated to extreme temperatures. The planet's atmosphere is so hot that most molecules are unable to survive on the blistering day side of the planet, where the temperature is 4,600 degrees Fahrenheit. Therefore, clouds probably cannot form to reflect light back into space. Instead, incoming light penetrates deep into the planet's atmosphere where it is absorbed by hydrogen atoms and converted to heat energy.

"We did not expect to find such a dark exoplanet," said Taylor Bell of McGill University and the Institute for Research on Exoplanets in Montreal, Quebec, Canada, lead researcher of the Hubble study. "Most hot Jupiters reflect about 40 percent of starlight."

But the planet's nighttime side is a different story. WASP-12b has a fixed day side and night side because it orbits so close to the star that it is tidally locked. The nighttime side is more than 2,000 degrees Fahrenheit cooler, which allows water vapor and clouds to form. Previous Hubble observations of the day/night boundary detected evidence of water vapor and possibly clouds and hazes in the atmosphere. WASP-12b is about 2 million miles away from its star and completes an orbit once a day.

"This new Hubble research further demonstrates the vast diversity among the strange population of hot Jupiters," Bell said. "You can have planets like WASP-12b that are 4,600 degrees Fahrenheit and some that are 2,200 degrees Fahrenheit, and they're both called hot Jupiters. Past observations of hot Jupiters indicate that the temperature difference between the day and night sides of the planet increases with hotter day sides. This previous research suggests that more heat is being pumped into the day side of the planet, but the processes, such as winds, that carry the heat to the night side of the planet don't keep up the pace."

The researchers determined the planet's light-eating capabilities by using Hubble's Space Telescope Imaging Spectrograph to search in mostly visible light for a tiny dip in starlight as the planet passed directly behind the star. The amount of dimming tells astronomers how much reflected light is given off by the planet. However, the observations did not detect reflected light, meaning that the daytime side of the planet is absorbing almost all the starlight falling onto it.

First spotted in 2008, WASP-12b circles a Sun-like star residing 1,400 light-years away in the constellation Auriga. Since its discovery, several telescopes have studied the exoplanet, including Hubble, NASA's Spitzer Space Telescope, and NASA's Chandra X-ray Observatory. Previous observations by Hubble's Cosmic Origins Spectrograph (COS) revealed that the planet may be downsizing. COS detected material from the planet's super-heated atmosphere spilling onto the star.

The results appear in the Sept. 14 issue of The Astrophysical Journal Letters.

https://www.nasa.gov/feature/goddard/2017/hubble-captures-blistering-pitch-black-planet

Offline CuddlyRocket

Re: Exoplanets And Stars Thread
« Reply #208 on: 09/15/2017 10:22 PM »
Bayesian Analysis of Hot Jupiter Radius Anomalies: Evidence for Ohmic Dissipation? (arXiv)

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The cause of hot Jupiter radius inflation, where giant planets with Teq >1000 K are significantly larger than expected, is an open question and the subject of many proposed explanations. Rather than examine these models individually, this work seeks to characterize the anomalous heating as a function of incident flux, ϵ(F), needed to inflate the population of planets to their observed sizes. We then compare that result to theoretical predictions for various models. We examine the population of about 300 giant planets with well-determined masses and radii and apply thermal evolution and Bayesian statistical models to infer the anomalous power as a function of incident flux that best reproduces the observed radii. First, we observe that the inflation of planets below about M=0.5MJ appears very different than their higher mass counterparts, perhaps as the result of mass loss or an inefficient heating mechanism. As such, we exclude planets below this threshold. Next, we show with strong significance that ϵ(F) increases with Teq towards a maximum of ∼2.5% at Teq≈1500 K, and then decreases as temperatures increase further, falling to ∼0.2% at Teff=2500 K. This high-flux decrease in inflation efficiency was predicted by the Ohmic dissipation model of giant planet inflation but not other models. We also explicitly check the thermal tides model and find that it predicts far more variance in radii than is observed. Thus, our results provide evidence for the Ohmic dissipation model and a functional form for ϵ(F) that any future theories of hot Jupiter radii can be tested against.

It's interesting that exoplanet studies are quickly finding these apparent physical boundaries separating planets into different classes.

Offline Star One

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Exoplanets And Stars Thread
« Reply #209 on: 09/17/2017 07:05 PM »
Diamonds Really Do Rain on Neptune, Experiments Conclude

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Researchers subjected hydrocarbon samples in a laboratory to Neptune-like pressures. The samples, reminiscent of molecules found in the ice giant’s atmosphere, compressed into nanodiamonds.

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Knowing how hydrocarbons might behave deep within an ice giant’s atmosphere will affect our understanding of how atmospheres transport heat and evolve over time, explained Kraus. What’s more, the implications of this research extend beyond our solar system to exoplanets, as a large fraction of the known exoplanets are similar in size or mass to our ice giants.

The ability to model an ice giant atmosphere’s density from the top down to the core is a critical part of characterizing that planet. For example, an atmosphere made mostly of hydrogen is much puffier than one with diamonds, Kraus noted.

A diamond-studded atmosphere also likely behaves very differently than one without diamonds. For example, atmospheric convection might have to overcome more hurdles, which may lead to sharp changes in chemical composition between different atmospheric layers, the researchers said. This could also inhibit heat flow.

“These experiments can be used to improve our understanding of the behavior of common materials in the universe at high pressures and temperatures, which has a direct connection to modeling planetary interiors,” said Ravit Helled, a computational science and theoretical astrophysics professor at the University of Zurich in Switzerland, who was not involved in the study.

https://eos.org/articles/diamonds-really-do-rain-on-neptune-experiments-conclude
« Last Edit: 09/17/2017 07:08 PM by Star One »

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #210 on: 09/18/2017 08:04 PM »
Do planets remember how they formed?

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One of the most directly observable features of a transiting multi-planet system is their size-ordering when ranked in orbital separation. Kepler has revealed a rich diversity of outcomes, from perfectly ordered systems, like Kepler-80, to ostensibly disordered systems, like Kepler-20. Under the hypothesis that systems are born via preferred formation pathways, one might reasonably expect non-random size-orderings reflecting these processes. However, subsequent dynamical evolution, often chaotic and turbulent in nature, may erode this information and so here we ask - do systems remember how they formed? To address this, we devise a model to define the entropy of a planetary system's size-ordering, by first comparing differences between neighboring planets and then extending to accommodate differences across the chain. We derive closed-form solutions for many of the micro state occupancies and provide public code with look-up tables to compute entropy for up to ten-planet systems. All three proposed entropy definitions exhibit the expected property that their credible interval increases with respect to a proxy for time. We find that the observed Kepler multis display a highly significant deficit in entropy compared to a randomly generated population. Incorporating a filter for systems deemed likely to be dynamically packed, we show that this result is robust against the possibility of missing planets too. Put together, our work establishes that Kepler systems do indeed remember something of their younger years and highlights the value of information theory for exoplanetary science.

https://arxiv.org/abs/1709.04987

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #211 on: 09/18/2017 08:30 PM »
New supernova analysis reframes dark energy debate

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The accelerating expansion of the universe may not be real, but could just be an apparent effect, according to new research published in the journal Monthly Notices of the Royal Astronomical Society. The new study — by a group at the University of Canterbury in Christchurch, New Zealand — finds the fit of Type Ia supernovae to a model universe with no dark energy to be very slightly better than the fit to the standard dark energy model.

https://astronomynow.com/2017/09/18/new-supernova-analysis-reframes-dark-energy-debate/

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #212 on: 09/21/2017 04:03 PM »
The empty primordial asteroid belt

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Abstract
The asteroid belt contains less than a thousandth of Earth’s mass and is radially segregated, with S-types dominating the inner belt and C-types the outer belt. It is generally assumed that the belt formed with far more mass and was later strongly depleted. We show that the present-day asteroid belt is consistent with having formed empty, without any planetesimals between Mars and Jupiter’s present-day orbits. This is consistent with models in which drifting dust is concentrated into an isolated annulus of terrestrial planetesimals. Gravitational scattering during terrestrial planet formation causes radial spreading, transporting planetesimals from inside 1 to 1.5 astronomical units out to the belt. Several times the total current mass in S-types is implanted, with a preference for the inner main belt. C-types are implanted from the outside, as the giant planets’ gas accretion destabilizes nearby planetesimals and injects a fraction into the asteroid belt, preferentially in the outer main belt. These implantation mechanisms are simple by-products of terrestrial and giant planet formation. The asteroid belt may thus represent a repository for planetary leftovers that accreted across the solar system but not in the belt itself.

http://advances.sciencemag.org/content/3/9/e1701138

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #213 on: 09/22/2017 09:22 AM »

Astronomers Have Spotted a Strange Hybrid Asteroid in Our Solar System

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The Hubble space telescope has seen a lot of weird things that defy easy definition. Here's one more for the list – a binary asteroid that's also a comet.

Astronomers have found a pair of them, in fact, swirling around one another in the asteroid belt while leaving a stream of dust in their wake. Not only is it a beautiful example of how nature DNGAF about our categories, it raises some interesting questions on how many of these hybrids might be out there.

The binary object itself was first spotted back in 2006 as part of the asteroid-searching Spacewatch program, resulting in it getting the not-so-glamorous name 2006 VW139.

It wasn't until 2012 that astronomers realised something odd about it; this thing that was an asteroid with comet-like characteristics, namely a streaming tail.

So-called main belt comets aren't new, but they're by no means common either. This asteroid is just one of about a dozen such objects ever discovered.

What makes this particular one so unique is that it's in two pieces.

2006 VW139 is made of a pair of equal-sized lumps orbiting one another at a distance of just under 100 kilometres (about 60 miles).

http://www.sciencealert.com/astronomers-spotted-a-weird-new-object-in-asteroid-belt-and-it-s-gorgeous

Offline Star One

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Re: Exoplanets And Stars Thread
« Reply #214 on: 09/22/2017 04:46 PM »
A Fast Radio Burst Occurs Every Second throughout the Observable Universe

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Abstract
Recent multi-telescope observations of the repeating fast radio burst (FRB) FRB 121102 reveal a Gaussian-like spectral profile and associate the event with a dwarf metal-poor galaxy at a cosmological redshift of 0.19. Assuming that this event represents the entire FRB population, we make predictions for the expected number counts of FRBs observable by future radio telescopes between 50 MHz and 3.5 GHz. We vary our model assumptions to bracket the expected rate of FRBs and find that it exceeds one FRB per second per sky when accounting for faint sources. We show that future low-frequency radio telescopes, such as the Square Kilometre Array, could detect more than one FRB per minute over the entire sky originating from the epoch of reionization.

http://iopscience.iop.org/article/10.3847/2041-8213/aa8905/meta